The Darknet holds various Markets which allow the registered users to obtain goods.
A lot of the goods which are found on the Darknet markets are illegal and they could be dangerous but there are more than only goods which are available on the Darknet markets. On the Darknet markets various services are being provided.
The services can be literally anything. It can be a DDOS attack or an request to imitate/track someone (online).
One of the websites which keeps tracks of the Darknet markets is the dnstats.net project. This project has listed various Darknet Markets and extra Darknet sites on the website which they monitor daily.
The links to the marketplaces can be found via the dnstats.net website. The dnstats.net service keeps tracks of the Marketplaces on a daily basis, so you will have the working link if needed.